The present invention relates to a coupling and more particularly although not exclusively to a coupling for use in an orthotic brace, for example, a hip, is shoulder, wrist or ankle brace.
Known couplings of which the applicants are aware have not been as strong and rigid or as durable as may be considered desirable. For example, known ball and socket couplings that rely on set screws engaging the surface of the ball to locate the portions of the coupling are prone to slippage under bending stress, while the set screws deform and pit the surface of the ball and ultimately render it unserviceable.
In one aspect, the invention provides a coupling comprising first and second portions each comprising a planar bearing surface, a cam member having a first planar bearing face bearing rotationally on the planar bearing surface of the first portion and journalled thereto through a first journal bearing resisting lateral slippage, a second planar bearing face disposed in a plane inclined to the plane of the first bearing face and bearing rotationally toward the planar bearing surfaces of the second portion and journalled thereto through a second journal bearing resisting lateral slippage, and a clamping device urging said bearing surface toward said bearing faces of the cam member and generating a frictional reaction retaining each bearing surface in a selected rotational position with respect to the cam member.
Since the compressive forces are transmitted through opposing planar faces, great compressive stress can be applied and hence high frictional forces generated without permanently deforming the coupling elements. This provides a coupling of greatly improved strength characteristics. Further, the wedge-like cam member together with the slippage resistant journal bearings provide in effect a monolithic body in the clamped condition of the coupling, so as to provide a coupling with excellent rigidity and resistance to bending.